The Taco Switching Relay is the best choice for all your zoning needs, with advanced timer and boiler functions, external diagnostic lights, switchable priority and contractor friendly PC board layouts. Combined with the time proven reliability of the 00® family of circulators and thermostats, total system integration is achieved. Additional features include built-in priority protection, premium sealed relays, compact design, fuse protected, isolated end switch and universal thermostat compatibility.